For every type of motor in every situation or setting, the National Electrical Code (NEC) explains all requirements. The code book, available from the National Fire Protection Association (NFPA), is fairly extensive and all the requirements must be implemented (see Resources). The cost of the most-recent code book is $85, as of 2011.
Local municipalities are free to pass codes that rely upon the NEC, or may be stricter. For example, the city of Londonberry, New Hampshire, specifies conduit codes for pool pump motors. The city specifies heavy reliance on the NEC for all conduit and wiring to a pool.
The University of Tennessee, as another example, has set requirements for all electrical contractors performing work on campus. One of the requirements is that metal conduits are used to house motor wires, as opposed to plastic. The university also specifies all conduit and wiring must be in accordance with the NEC.
Motors run in size from 1/8 horsepower to 200 or more horsepower. Each has their unique needs. The NEC has already determined the needs of each motor, and designed the code accordingly. It is required of the qualified electrician or electrical designer to finalize the actual type of wire and conduit to use. A one-size-fits-all approach should never be taken. Each motor wiring and conduit is designed on a case-by-case basis.
A qualified electrician must always adhere to the latest code. Electrical technology changes as new materials and techniques are discovered. As an extreme example, an electrician would not use code from 1908. Wires were insulated with cotton rope then, and is invalid in 2011. The NFPA states that the next code book will be released in 2014. When the 2014 book is released, the 2011 edition will be outdated and should not be relied upon.